Unless otherwise indicated herein, the materials described herein are not prior art to the claims in the present application and are not admitted to be prior art by inclusion in this section.
Many communication devices and home information appliances such as personal computers electrically communicate with each other and/or internally via electrical cables, such as high-speed card cables, flexible print circuits and flexible flat cables. Some electrical cables used for electrical communication often include multiple signal lines, insulating tape, and adhesive.
Until recently, electrical communication using electrical cables occurred at relatively low speeds of several megahertz (“MHz”) or less. At relatively low speeds of several megahertz or less, characteristic impedance of the electrical cables has a relatively insignificant impact on signals transmitted by the electrical cable and can often be ignored when designing the electrical cables.
In recent years, communication devices supporting electrical communication at speeds of 100 MHz or more have become more prevalent. At speeds of 100 MHz or more, characteristic impedance has a more significant impact on signals transmitted by the electrical cable. For example, without careful design and control of the characteristic impedance of the electrical cable, the electrical cable may be unable to effectively transmit signals through the electrical cable.
In addition to including multiple signal lines, insulating tape and adhesive, electrical cables that support communication at speeds of 100 MHz or more can additionally include distributed constant circuits and a ground plane. The characteristic impedance of such electrical cables may be affected by the dimensions of the signal lines and ground plane, the thickness of the insulating tape and adhesive, a dielectric constant of the insulating tape, and/or other parameters.
Many electrical cables are flexible. The operating environment in which an electrical cable is implemented may dictate a desired amount flexibility for the electrical cable. Greater flexibility can often be achieved by making an electrical cable thinner. As an electrical cable is made thinner, the distance between the signal lines and the ground plane decreases, the capacitance between the signal lines and the ground plane increases and the characteristic impedance of the electrical cable is changed.
One way to make an electrical cable thinner while keeping the characteristic impedance of the electrical cable at a desired value is to decrease the distance between the signal lines and the ground plane and decrease the width of the signal lines. However, reducing the width of the signal lines in an electrical cable inevitably leads to power loss caused by electric resistance (attenuation) and an increase in DC resistance. Thus, increasing the flexibility of an electrical cable by decreasing the distance between the signal lines and ground plane and maintaining characteristic impedance of the electrical cable at a particular value by decreasing the width of the signal lines results in an electrical cable that may not be suitable for communication at speeds of 100 MHz or more.